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Free access article

Issue A&A
Volume 413, Number 2, January II 2004
Page(s) 609 - 622
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20031572



A&A 413, 609-622 (2004)
DOI: 10.1051/0004-6361:20031572

Sulphur-bearing species in the star forming region L1689N

V. Wakelam1, A. Castets1, C. Ceccarelli1, 2, B. Lefloch2, E. Caux3 and L. Pagani4

1  Observatoire de Bordeaux, BP 89, 33270 Floirac, France
2  Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
3  CESR CNRS-UPS, BP 4346, 31028, Toulouse Cedex 04, France
4  LERMA & FRE 2460 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France

(Received 10 June 2002 / Accepted 7 October 2003 )

Abstract
We report observations of the expected main S-bearing species (SO, SO 2 and H 2S) in the low-mass star forming region L1689N. We obtained large scale (~ $300'' \times 200''$) maps of several transitions from these molecules with the goal to study the sulphur chemistry, i.e. how the relative abundances change in the different physical conditions found in L1689N. We identified eight interesting regions, where we carried out a quantitative comparative study: the molecular cloud (as reference position), five shocked regions caused by the interaction of the molecular outflows with the cloud, and the two protostars IRAS 16293-2422 and 16293E. In the cloud we carefully computed the gas temperature and density by means of a non-LTE LVG code, while in other regions we used previous results. We hence derived the column density of SO, SO 2 and H 2S, together with SiO and H 2CO - which were observed previously - and their relevant abundance ratios. We find that SiO is the molecule that shows the largest abundance variations in the shocked regions, whereas S-bearing molecules show more moderate variations. Remarkably, the region of the brightest SiO emission in L1689N is undetected in SO 2, H 2S and H 2CO and only marginally detected in SO. In the other weaker SiO shocks, SO 2 is enhanced with respect to SO. We propose a schema in which the different molecular ratios correspond to different ages of the shocks. Finally, we find that SO, SO 2 and H 2S have significant abundance jumps in the inner hot core of IRAS 16293-2422 and discuss the implications of the measured abundances.


Key words: ISM: abundances -- ISM: molecules -- stars: formation -- ISM: individual objects: L1689N -- ISM: individual objects: IRAS 16293-2422

Offprint request: V. Wakelam, wakelam@observ.u-bordeaux.fr

SIMBAD Objects in preparation



© ESO 2004

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